Method of cleaning coal



. E- TRENT.

METHOD OF CLEANING COAL.

APPLICATION FILED JULY 9,1919.

Patentad June 2% 1922,,

ice.

WALTER E. TRENT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR. T0 TRENT PROCESS CORPORATION, OF WILMINGTON, DELAWARE. A CORPORATION OF DELA- WARE.

ll .elJZOJ 63.

s ecification of Letters Patent. Patented June 21), 19*" METHOD or CLEANING COAL.

hi it u Application filed m 9, 1919. Serial No. 309.642.

To (1]! whom it may concern:

Be it known that I, W ALTER E. TRENT, a citizen of the United States, residing at \Vashington, in the District of Columbia,

such as silica, silicates, iron and sulphur,

etc, that are thoroughly incorporated with and form a part of the coal, these impurities being the ash or clinker forming substances when the coal is'burned. These impurities or substances'are of an entirely different class than the stone whichgets mixed with the coal during mining, such as slate or the like from the walls of a coal vein. Such materials dilute the coal but are not inherent or combined impurities and consequently can be washed from the coal by the ordinary coal washing methods. I

So far as I am aware, it has never been attempted to physically separate the carbonaceous contents from the impurities of coal,

it having been the practice to leave the inherent impurities in the coal and to only remove foreign substances. which are not physically combined with the coal as it has generally been thought that a chemical-union existed between the carbonaceous and impure substances of the coal to such an extent as to prevent their separation. These inherent impurities or substances form ash and clinkers when the coal is burned, and when the coal is used in pulverized form the impurities form deposits that adhere to the method ,of removing from the coal the troublesome inherent or intrinsic impurities that are incorporated therewith and form a part of the coal, which impurities are the ash forming; materials when the coal is burned. the ash forming materials being rcferred to herein as impurities inasmuch as theyvare not considered to be the carbonaceous contcnt of the coal. but in themselves they may of course be substances of pure iron, sulphide. silica or the like. l have found these impurities to occur in very minute particles distributed throughout the bodyof coal. and in contradistinction to the generally accepted theory that these impurities are inseparably united to the carbonaceous matter-,1 have discovered that they may be physically detached or freed from the carbonaceous material by connninuting' thecoal which brings about a liberation of the troublesome ash forming content from the other substances of the coal. To effect a separation of the liberated or freed ash forming substances from the carbonaceous material. the mass is then introduced into a separator to remove the impure substances from the carbonaceous content of the coal, which carbonaceous content free of troublesome impurities is then used as a fuel in an inmalpable powder of approximately a 200 mesh or liner. which reduction results in .a detachment of the carbonaceous or combustible content from other substances forming the coal.

The burning of coal in powdered form is now looked upon with favor. it having been recognized that the same possesses many advantages. but in grinding the coal to an impalpahlc powder additional impurities are often intrmluced thereto. it having been found that if ball mills are used, very fine particles of iron resulting from the wear of the balls mixed with the reduced coal, or if pebble mills are employed, the particles of flint from the wear of the pebbles become associated with the coal. these impurities being just as detrimental and undesirable as the inherent impurities of the coal, and it is an object of this method to remove these as well as the inherent impurities prior to burning of the coal.

In carrying out the present method. the coal after havin been coarsely ground and separated from foreign impurities of the nature of slate, stones, or the like, which become mixed with the coal, is then finely "ground to' an approximately 200 mesh or from the carbonaceous orv combustible content of the coal. After the impurities have thus been liberated, the entire mass is then introduced to a separator to cause the car- 'bonaceous material to be separated in its finely divided state from all inherent as well as foreign impurities if they become associated with the coal during its grinding or otherwise, the coal after this separation being in condition for burning.

The coal, when introduced to the grinder, is usually mixed with water or another liquid, and after being ground and classified to such a fine degree as to liberate the inherent impurities, the'emulsion, consisting of separated inherent substances, carbonaceous materials, foreign impurities and the water, is conveyed to a separator where; in the carbonaceous or combustible materials are suspended in the water and run off therein to a point of collection, while the impurities are collected in the separator.

In separating the carbonaceous materials from the heavier or impure substances, the emulsion is conveyed to a separating apparatus, the carbonaceous particles traveling with the water overflow from the apparatus by reason of the current carrying the same in suspension while the heavier substances settle. Such impurities that float by reason of floculent conditions, flakiness surface tension, or for other reasons, and there are such substances in'coal that act in such a manner, notably iron and sulphur. float out of the separator suspended in the water with the carbonaceous materials, but in the apparatus in which the carbonaceous particles are collected, the velocity of the water currents is reduced to such a slow. travel that the carbonaceous materials settle, but the floating floculent and flaky substances above mentioned travel in suspension in the water and are washed away therein.

In following the method, it is usually preferable to convey the emulsion from the separator in which the impurities deposit to an apparatus for thickening or collecting the carbonaceous materials while the surplus water with the floating impurities is permitted to escape. From this apparatus the thick liquid carbonaceous material is withdrawn, being free from all impurities both foreign and inherent. The carbonaceous material is then in condition for burning as an'emulsion of coal and water, it being also contemplated in the present method to tional type, so as to reduce the coal to lumps of any desired size, foreign substances that become mixed with the coal during its mining, such as slate or the like, being removed therefrom after its grinding. The coal thus ground is delivered fromthe grinding mill through a chute 1 into a hopper 1 which receives a supply of water in addition to the coal, the water and coal being fed by means of the revolving feeding cups 2 rotating in the hopper 1 into the interior of the tube mill 3, which is rotatably mounted upon the trunnions 4 supported by the standards 5. The tube mill is rotated by means of a driving Wheel 7 around which a belt or the like passes, the driving wheel being mountedupon' a shaft 7 carrying a spur gear 8 meshing with the ring gear 9 surrounding the tubemill. The mill may be of any preferred construction preferably having disposed therein a plurality of iron balls or pebbles as is usual-in mills of this type, it being manifest that upon a rapid rotation of the tube, the balls and pebbles reduce the coal or pulverize it to an impalpable mass. hen .the coal is introduced to the tube mill with the water by the action of the feeding cups 2 for delivering the coal to the interior of the mill, the same is allowed to remain therein until a thorough pulverizing has taken place, the coal being reduced to such a fineness as to physically separate or break away the minute inherent impurities thoroughly incorporated therein, such as silica, silicates, iron or sulphur, which are the ash forming substances of the coal when burned from the carbonaceous or combustible content of the coal. It will be understood that by the terms inherent orintrinsic impurities or ash forming materials, as used throughout the specification, it is meant that these impurities are materials of a different nature from the carbonaceous content of the coal and are, as a general thing, insoluble, although not always so. While it is, of course, understood that the substance re.-

ferred' to as inherent impurities may not, in

themselves, be impure, thatis, they may be pure particles of iron, sulphide or the like, they are regarded as impurities so far as the carbonaceous content of the coal is concerned; and it isthis class of impurities, as well asslate or other extraneous impurities, that become mixed with the coal when mined or during its treatment that the present method contemplates to remove from the carbonaceous materials.

After'undergoing treatment in the tube mill so as to bring about a physical separationot the inherent or intrinsic materials or substances from the carbonaceous or combustible content of the coal which is the result of grinding the coal to a much finer degree than has heretofore been practiced,the water carrying the carbonaceous content of the pulverized coal, the separated inherent or natural impurities and other foreign impurities through the gudgeon 7 of the mill into the trough 8' from where it is delivered into a classifier 9 which may be of any preferred construction, the present'showing consisting of a classifier having a discharge chute 9 for the finely divided particles and water, while the larger particles of coal and impurities discharged from the tube mill are not permitted to escape through the discharge 9, but are carried through the classi tier by the reciprocating scraper 10 and redelivered to the trough 1 to be again fed to the tube mill for further grinding, these particles having been groundv too coarse to liberate the impurities from the carbonaceous content of the coal. The scraper 10 is actuated by means of the link members 11 cooperating with the bell crank lever 12 and the driving lever 13 on the driving shaft 14 that is operated by a belt on the pulley 15 from any source of power, the operation of this shaft serving to cause a reciprocation of the scrapers slowly upon the surface of the classifier to deliver the coarse material back to the feed trough.

The finely divided carbonaceous materials and impurities include any foreign sub stances which may be particles of iron from the ball grinders or flint from the pebbles passing from the classifier through the feed chute 9' which are discharged into the trough 16 to be delivered to a separator 17 through a central pertoated sleeve 17 to the interior of the separator. It will be understood that at'ter passing through the tube mill the coal has been ground to such a fine degree that the inherent impurities or substances are entirely liberated from the carbonaceous materials, so that the freed particles of carbonaceous granules and impurities are emulsified in the water and delivered to the separator. The emulsion is delivered to the separator through the sleeve so as to prevent a disturbance of the surface of the material in the separator and to assist in separating the insoluble impure substances from the coal, a perforated pipe 18 is disposed within the separator with its lower portion in communication with the suction pump 19 discharging into the pipe 20 leading to the spray or discharge nozzles 21 of the agitator 22. This agitator slowly revolves. the emulsion being drawn through the pipe 18 and .These carbonaceous materials and water when reaching the top of the separator flow out through the overflow trough 24; extending entirely therearound and into a trough 25 to the settling tank 26. The material is continuously introduced to the separator, and therefore, continuously flows therefrom through the trough 25 to the settling tank when the impure substances that have been physically separated from the carbonaceous content of the coal in the tube mill are allowed to deposit in the separator, these substances being removed through the valve controlled discharge pipe 26 at any desired time. Vl hile I have shown this form of separator in carrying out the present method, it will be understood that any other separator, such as a filtering process or the like can be used, so long as the liberated particles of impure substances are separated or removed from the carbonaceous materials.

The thickening or settling tank 26 is formed with a plurality of rakes 25 mounted upon a slowly revolving shaft 28, and the emulsion which is substantially free of most impurities and consists of the carbon contents of the coal and water; is introduced to this tank to thicken. The tank is quite large, as disclosed in the drawings, and the water when entering the same loses its velocity, allowing the coal to settle while any fioculent impurities that are suspended in the water or will float therewith are carried with the discharged water into the feed lander 26 into a discharge pipe 29. As the carbonaceous contents of the coal settles in the settling or collecting tank 25 and becomes somewhat thickened it is discharged through the discharge pipe 26 to be used in a powdered form for burning with or without water or to be dried and formed into briquettes or as may be desirable for other uses.

The accumulated insoluble and other substances in the separating tank 17 are conveyed therefrom to the discharge pipe 26. it will be understood. however. that the carbonaceous or combustible content of the coal after passing through the liquid sepa rator 17 is free of any impurities both inherent and foreign and after being collected in the collecting tank 25 in a thickened or paste form is in a pure state so that the same may be burned in a powdered form in a boiler or the like without the objectionable feature of insoluble matters forming deposits upon the boiler walls or tubes.

In practicing the present method, the 'following steps are usually employed:

The coal is' first ground in a grinding mill to any desired size, usually having such foreign impurities as slate, stones, or

the like removed therefrom by screening, picking and washing, as is now the usual practice in cleaning coal. When in this condition, the mass of coal is introduced to a ball mill or any other improved reducer and finely pulverized to an impalpable mass of such a fine state of division as to detach the minute particles of ash forming materials from the carbonaceous contents of the coal. The ash forming materials, the carbonaceous contents of the coal and water are then thoroughly intermixed, torform an emulsion, being deli-vered in this form to a separating tank.

soas to collect the impurities that have become detached from the carbonaceous materials, trapping the same in the tank and allowing the substantially pure carbonaceous materials to flow with the water, because of a slight. current imparted thereto, to a collecting apparatus. It will be understood that before discharging the emulsion to ,a separator, the coal is classified so as to return any-particles that are not of a proper state of division as to detach the impurities back to the ball mill for further reduction. The water flowing from the separator has a slight current, the carbonaceous materials traveling therewith by reason of the current carrying the same in suspension while the heavier substances or impurities settle in the separator. Some impurities float by reason of floculent conditions, flakiness, or the like, with the water from the separator, but in the thickening apparatus the carbonaceous materials collect because of a reduction of the water current while the floculent impurities flow out to a point of discharge with the water. When the carbonaceous material suspended in the water enters the thickening appara tus, the coal settles and thickens, being withdrawn therefrom in a paste form. Af-

ter its withdrawal,-the mass may be dried or used in powdered form as a fuel, produclng no ashes orcllnkers whenburned, as the entire contents thereof are combustible, or the mass may be made in briquette .form.

In my cO-pending application, Serial No.

286,023, I have disclosed a method of burning pulverized coal by mixing the same with water to form an emulsion, but it has been found that pulverized coal thus .burned, if not freed of its inherent impurities will result in the accumulation of insoluble matters uponthe different parts of the furnace and boiler tubes, and after removing these impurities from the coal, as described in this method, the powdered coal may be fed to a furnace for burning in the carbonaceous matter from the carbonaceous fuel content of the coal, and in then subjecting the impalpable mass to a mechanical separation to separate detached impurities from the fine carbonaceous fuel matter. I I 3. The process of purifying coal. which comprises reducing coal to an impalpable powder to physically detach inherent noncarbonaceous matter from the carbonaceous content of the coal, and in then separating the detached non-carbonaceous impurities from the fine carbonaceous fuel.

4. The process of purifying coal, which comprises reducing coal to at least adegree of approximately 200 mesh to physically detach inherent non-carbonaceous impuritiesfrom the carbonaceous content of the coal, and in then separating the fine .detached impurities from the carbonaceous fuel matter.

In testimony whereof I hereunto afiix my signature in the presence of two witnesses.

WALTER E. TRENT.

Witnesses:

CHARLES-M. THOMAS, JAMES L. CRAWFORD. 

